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Boss is a large, brown horned beetle with tusk-like pincers. He has pink fur behind his head. He also bears the insignia of the Marines on his right side, which Yoko painted on his shell after befriending him. After molting, he grew in size, changed color into teal, and the fur behind his head became light green. His tusks also became bigger and gained a second set of points, and now featured small openings in the front, from out of which he could breathe fire.

When he initially met Yoko, Boss was a lot smaller and had a shiny, caramel-colored body, before molting and growing larger. It was around this time that Yoko gave him his Marines marking, which Boss somehow manages to preserve after molting.

Boss is a very brave and intelligent beetle. He is willing to protect Little East Blue and its inhabitants at any cost, even to the point where he tried to give himself up to the Amigo Pirates to spare everyone else. He also has a very strong bond with Yoko, a young girl who lost her father to pirates.

Unlike regular beetles, Boss continues to grow and to change shell even as an adult, this causing his unusual giant dimensions. He becomes stronger every time he grows up (once a month), making him a very powerful fighter, capable of emitting fire from his horn.

He has an incredible stamina, which allowed him to resist to Franky's Coup de Vent and Luffy's Gomu Gomu no Bazooka without serious wounds, and Yoko said that he can heal quickly overnight underground by incubating.

According to the Amigo Pirates, he was a runaway from Shiki the Golden Lion, who had been creating an army of super animals to take over the world.

Boss and Yoko together.

He lived in Little East Blue with Yoko, an orphan girl who found him in the forest some time after her father's death and got attached to the beetle seeing her lost father in him. Since then, Boss protected the island from the pirates.

Before finding out that Yoko was his owner, Luffy wanted to capture it and have it be their 10th member of his pirate crew. He later dropped this idea after seeing Yoko's determination, yet challenged Boss to a fight after he became stronger, something he agreed to.

When he was preparing for the evolution, Little East Blue was attacked by the Amigo Pirates, who wanted to capture him as a gift for Shiki. After being defeated by Largo and Corto, Boss agreed to follow the pirates to save the island from the hands of the Amigo Pirates, but was stopped by Luffy who wanted to continue their challenge.

After being hit by Straw Hat, Boss molted into a new form and attacked the pirates again, managing to free Luffy, Zoro and Sanji from their nets, but falling again under the attacks of Largo because his mutation had been too fast and his power was not completely restored. Freed from the net by Zoro, Boss was able to regain some of his power, which he used to defeat Corto first, and then to rescue Luffy and Brook who had fallen into the ocean after their battle with Largo.

He and the Straw Hats' captain eventually had their match, but it ended in a draw since none of them wanted to give up. In the end, Boss stayed with Yoko and the other inhabitants of Little East Blue, continuing his work as their protector, though Luffy did promise as he was leaving they would continue their fight again someday.